\documentclass{standalone}
\usepackage{tikz}
\usepackage{ctex,siunitx}
\setCJKmainfont{Noto Serif CJK SC}
\usepackage{tkz-euclide}
\usepackage{amsmath}
\usepackage{wasysym}
\usepackage{circuitikz}
\usetikzlibrary{patterns, calc}
\usetikzlibrary {decorations.pathmorphing, decorations.pathreplacing, decorations.shapes,}
\ctikzset{bipoles/length=1cm}
\begin{document}
\small
\begin{circuitikz}[>=latex, yscale=1.0,european]
  % \useasboundingbox(0.9,0)rectangle(5.1,5);
  \draw(0,1) to [battery2,name=dc] (5,1) to [rmeter, t=A, -*](5,2) -- (5,3);
  \node at (dc.left)[below left]{$\mathcal{E}\;  r$};
  \draw (5,2) to  [R=$R_2$] (1.5,2);
  \draw (5,3) to  [R=$R_1$] (1.5,3);
  \draw [fill=white](1.5,2) circle (2pt) node [above]{2};
  \draw [fill=white](1.5,3) circle (2pt)node [above]{1};
  \draw [very thick](.9,2.5)--(1.5,2.9);
  \draw (0,1)--(0,2.5)--(.9,2.5)node [below]{$K$};
  \draw [fill=white](.9,2.5) circle (2pt);
\end{circuitikz}
\end{document}